In a surface-mount-type semiconductor device, a plurality of electrode pads electrically connected to an internal circuit are disposed at the mounting-surface-side and the electrode pads are respectively electrically connected to bump electrodes. Usually, a barrier metal is provided between an electrode pad and a bump electrode to suppress reaction between and strengthen adhesion between the electrode pad and the bump electrode. A semiconductor device is mounted on a mounting board or the like via such bump electrodes disposed at the mounting-surface-side.
A method for manufacturing such bump electrodes has been suggested, which includes selectively depositing a barrier metal and a bump electrode material on electrode pads by sputtering, plating, or the like and melting the bump electrode material to obtain bump electrodes of a particular shape. Such a structure is disclosed in, for example, Japanese Laid-open Patent Publication Nos. 1997-199505, 1996-45941, and 2004-174538.
Existing semiconductor devices have had the following problem. That is, the height of the bump electrodes produced by the existing method inadvertently vary in some cases. The cause of such a height variation is presumably the difference in flowability between the bump electrode material and the material that makes up the periphery of the bumps, i.e., the difference in flowability caused by wettability. When the heights of the bump electrodes vary as such, failures such as poor connection between the device and the mounting substrate and an increase in resistance may occur.
In this respect, it has been difficult to form bump electrodes of uniform height on electrode pads by the existing methods for manufacturing semiconductor devices.